We have designed and constructed a retinal reflection densitometer that permits measurements of visual pigment changes and visual thresholds with the same apparatus. With it, we have made direct comparisons between human cone pigment density and visual threshold under identical experimental conditions in the fovea following complete bleaches of the cone pigments. Pigment regeneration and threshold recovery follow similar time courses under these conditions, implying that thresholds are limited by the ability of the cones to catch photons. But a problem has arisen. Larger stimulus diameters require less retinal illuminance for absolute threshold, yet cone pigment concentrations are found to have greater concentrations in the central fovea, apparently because cone outer segments are longer there. Central cones with their higher pigment concentrations, still yield better thresholds when they are included in larger areas. Areal summation therefore outweighs the advantage of increased pigment density for absolute threshold in the fovea.